In a long term evolution advanced (LTE-A) system, to improve throughput of cells and eliminate interference between subscribers, each cell may be configured with 16, 32, 64, or more transmitting antennas to perform beam shaping. A base station configures channel state information reference signals (CSI-RSs) for each user equipment (UE). Each UE uses the CSI-RSs to measure channel state information (CSI) of a channel, and then provides feedback to the base station. Since before the 3rd Generation Partnership Project (3GPP) release 12, a CSI-RS design is made based on the actual number of physical antennas, and up to 8 ports are involved in a CSI-RS before 3GPP release 12, therefore, each physical resource block may occupy up to 8 resource units, as shown in FIG. 1. However, currently, the number of physical antennas has largely increased, and if the number of CSI-RS ports is still designed based on the number of physical antennas, resources occupied by CSI-RSs in each physical resource block will significantly increase. Thus, it is an issue yet to be solved regarding how to reduce resources occupied by CSI-RSs as many as possible.
In a LTE-A system, CSI-RS resources are configured for UEs to measure channel state information which consists of rank indicator (RI), channel quality indicator (CQI), precoding matrix indicator (PMI), etc. At present, when CSI-RSs are sent from a base station to a UE, corresponding raw signals of the CSI-RSs are directly transmitted within an overall downlink system bandwidth, as shown in FIG. 2. By measuring the CSI-RSs, the UE obtains channel state information consisting of RI, CQI, and PMI. To be specific, a method to measure a CQI is first measuring the CSI-RSs to estimate channel information, and then assuming that specified PMI and RI are used to measure a corresponding CQI at a signal transmitting end, i.e., the CQI being measured based on the specified PMI.
When the number of antennas in the system increases rapidly, CSI-RS resources needed also increase rapidly. Therefore, it is necessary to provide channel state information to the base station as detailedly as possible, and meanwhile reduce occupation of CSI-RS resources as much as possible. By precoding CSI-RSs, CSI-RS transmission performance can be improved, which further improves accuracy of reference signal channel estimation, and improves system performance. In addition, by precoding the CSI-RSs, the number of CSI-RS ports can be reduced, so as to reduce resources occupied by the CSI-RSs. Here, a CSI-RS is precoded using a precoding matrix before it is sent to a UE, and therefore, channel information estimated out based on a CSI-RS measurement is equivalent channel information. Through this equivalent channel information, channel state information (consisting of RI, PMI, and CQI) with the precoding matrix being used can be obtained. Therefore, it is necessary to provide an effective technical scheme to provide suitable CSI-RS resource configuration.